1. Field of the Invention
This invention relates to a method and apparatus for recording and reading out images, wherein an image is recorded by use of an anisotropic fluorescent material screen.
2. Description of the Related Art
Apparatuses utilizing two-dimensional image read-out means, e.g. facsimile apparatuses, copying machines, and radiation image sensors, have heretofore been known.
For example, in the fields of medical radiation image sensors, and the like, methods and apparatuses for recording and reading out radiation image information, wherein two-dimensional image read-out means is utilized, have heretofore been proposed. With the proposed methods and apparatuses for recording and reading out radiation image information, such that a radiation dose delivered to an object during a medical radiation image recording operation may be kept small, and such that the image quality of an image and its capability of serving as an effective tool in, particularly, the efficient and accurate diagnosis of an illness may be enhanced, a solid-state radiation detector (an electrostatic recording material), which is provided with a photo-conductive material (layer) sensitive to radiation, e.g. X-rays, such as a selenium plate, is employed as the two-dimensional image read-out means. The solid-state radiation detector is exposed to radiation, such as X-rays, carrying radiation image information, and electric charges in an amount proportional to the radiation dose delivered to the solid-state radiation detector are accumulated as latent image charges at a charge accumulating section in the solid-state radiation detector. In this manner, the radiation image information is recorded as an electrostatic latent image at the charge accumulating section. Thereafter, the solid-state radiation detector, in which the radiation image information has been recorded, is scanned with a laser beam or a light beam radiated out from a line light source, and the radiation image information is thereby read out from the solid-state radiation detector.
As the solid-state radiation detectors utilized as the two-dimensional image read-out means in the aforesaid methods and apparatuses for recording and reading out radiation image information, various types of solid-state radiation detectors have heretofore been proposed. For example, from the aspect of a charge forming process for generating the latent image charges, which carry image information, in the solid-state radiation detector, the solid-state radiation detectors may be classified into photo conversion types of solid-state radiation detectors, direct conversion types of solid-state radiation detectors, and improved direct conversion types of solid-state radiation detectors which belong to the category of the direct conversion types of solid-state radiation detectors and in which the latent image charges are read out through scanning with reading light. Also, from the aspect of a charge reading process for acquiring an image signal proportional to the amount of the latent image charges accumulated at the charge accumulating section, the solid-state radiation detectors may be classified into thin-film transistor (TFT) reading types of solid-state radiation detectors and photo reading types of solid-state radiation detectors.
With the TFT reading types of solid-state radiation detectors, TFT""s are operated successively in order to convert the latent image charges, which are accumulated at the charge accumulating sections, into a radiation image signal, and the radiation image signal is fed out. With the photo reading types of solid-state radiation detectors, a reading electromagnetic wave (ordinarily, visible light is employed as the reading electromagnetic wave) is irradiated to the solid-state radiation detectors in order to convert the latent image charges, which are accumulated at the charge accumulating section, into an image signal, and the image signal is fed out.
With the photo conversion types of solid-state radiation detectors, radiation is converted into light, and thereafter electric charges are generated with the light. For example, the photo conversion types of solid-state radiation detectors comprise two-dimensional image read-out means (i.e., solid-state radiation detecting means) and a fluorescent material (i.e., a scintillator) overlaid upon the two-dimensional image read-out means. The two-dimensional image read-out means comprises an insulating substrate and a plurality of photoelectric conversion devices (each having a charge accumulating section for accumulating electric charges to be detected), which are arrayed in a two-dimensional pattern on the insulating substrate. When the fluorescent material is exposed to radiation carrying image information, the fluorescent material produces visible light carrying the image information. The photo conversion types of solid-state radiation detectors are described in, for example, Japanese Unexamined Patent Publication Nos. 59(1984)-211263 and 2(1990)-164067, PCT International Publication No. WO92/06501, and xe2x80x9cSignal, Noise, and Read Out Considerations in the Development of Amorphous Silicon Photodiode Arrays for Radiotherapy and Diagnostic X-ray Imaging,xe2x80x9d L. E. Antonuk et al., University of Michigan, R. A. Street Xerox, PARC, SPIE Vol. 1443, Medical Imaging V; Image Physics (1991), pp. 108-119. The two-dimensional image read-out means employed in the photo conversion types of solid-state radiation detectors utilizes the TFT reading type of solid-state radiation detecting means. The two-dimensional image read-out means detects the fluorescence produced by the fluorescent material and accumulates the latent image charges, which carry the image information, at the charge accumulating sections of the photoelectric conversion devices. Also, the TFT""s, each of which is connected to one of the photoelectric conversion devices, are operated successively, the latent image charges accumulated at the charge accumulating sections are thereby converted into a radiation image signal, and the radiation image signal is fed out.
With the direct conversion types of solid-state radiation detectors, radiation is irradiated to a photo-conductive layer, and electric charges are generated directly in the photo-conductive layer. For example, the direct conversion types of solid-state radiation detectors comprise a photo-conductive layer, which exhibits electrical conductivity when it is exposed to recording radiation, and two-dimensional image read-out means. The two-dimensional image read-out means is constituted of a plurality of charge collecting electrodes, which are arrayed in two-dimensional directions and collect electric charges generated in the photo-conductive layer, and capacitors, each of which acts as a charge accumulating section and is connected to one of the charge collecting electrodes. The electric charges having been collected by each of the charge collecting electrodes are accumulated at the corresponding capacitor as the latent image charges carrying the image information. The direct conversion types of solid-state radiation detectors are described in, for example, (i) xe2x80x9cMaterial Parameters in Thick Hydrogenated Amorphous Silicon Radiation Detectors,xe2x80x9d Lawrence Berkeley Laboratory, University of California, Berkeley, Calif. 94720 Xerox Parc. Palo Alto. Calif. 94304; (ii) xe2x80x9cMetal/Amorphous Silicon Multilayer Radiation Detectors, IEE TRANSACTIONS ON NUCLEAR SCIENCE, Vol. 36, No. 2, April 1989; and (iii) Japanese Unexamined Patent Publication No. 1(1989)-216290. As in the photo conversion types of solid-state radiation detectors, the two-dimensional image read-out means employed in the direct conversion types of solid-state radiation detectors utilizes the TFT reading technique. Specifically, the TFT""s are operated successively, the latent image charges having been accumulated at the capacitors are thereby converted into a radiation image signal, and the radiation image signal is fed out.
The improved direct conversion types of solid-state radiation detectors have been proposed by the applicant in Japanese Patent Application Nos. 10(1998)-232824 and 10(1998)-271374. In the improved direct conversion types of solid-state radiation detectors, latent image charges are read out through the scanning with reading light. The improved direct conversion types of solid-state radiation detectors comprise:
i) a first electrical conductor layer having permeability to recording radiation,
ii) a recording photo-conductive layer, which exhibits electrical conductivity when it is exposed to the recording radiation having passed through the first electrical conductor layer,
iii) a charge transporting layer, which acts approximately as an insulator with respect to electric charges having a polarity identical with the polarity of electric charges occurring in the first electrical conductor layer, and which acts approximately as a conductor with respect to electric charges having a polarity opposite to the polarity of the electric charges occurring in the first electrical conductor layer,
iv) a reading photo-conductive layer, which exhibits electrical conductivity when it is exposed to a reading electromagnetic wave, and
v) a second electrical conductor layer having permeability to the reading electromagnetic wave,
the layers being overlaid in this order. In the improved direct conversion types of solid-state radiation detectors, latent image charges carrying image information are accumulated at a charge accumulating section, which is formed at an interface between the recording photo-conductive layer and the charge transporting layer. In the proposed improved direct conversion types of solid-state radiation detectors, the photo reading technique is employed for the acquisition of an image signal. The proposed improved direct conversion types of solid-state radiation detectors are not the ones which comprise a plurality of detecting devices distributed in two-dimensional directions. However, since the proposed improved direct conversion types of solid-state radiation detectors are scanned with reading light, which acts as a reading electromagnetic wave, the solid-state radiation detectors substantially act as the two-dimensional image read-out means.
Such that the sensitivity of the direct conversion types of solid-state radiation detectors and the improved direct conversion types of solid-state radiation detectors described above may be enhanced and images having good image quality may be obtained, i.e. such that the ratio of signal values, which are outputted from the solid-state radiation detectors, to the dose of radiation delivered to the solid-state radiation detectors may be enhanced, the applicant proposed the methods and apparatuses, wherein a fluorescent material screen having a high radiation absorption efficiency is located on the recording radiation irradiation side of the solid-state radiation detector, and an image recording and read-out operation is performed in this state. The methods and apparatuses utilizing the fluorescent material screen are proposed in, for example, Japanese Patent Application Nos. 10(1998)-232824 and 10(1998)-243379.
However, in cases where the fluorescent material screen is located in the manner described above and the image recording operation is performed in this state, the problems occur in that the light becomes blurred within the fluorescent material screen, the sharpness of the obtained image becomes low, and the image quality of the obtained image becomes bad.

The primary object of the present invention is to provide an image recording and read-out method wherein, in cases where an image recording and read-out operation is performed by utilizing a fluorescent material screen, problems with regard to deterioration of image sharpness are capable of being reduced.
Another object of the present invention is to provide an image recording and read-out method, wherein problems with regard to a moire phenomenon and unbalance between image sharpness in a main scanning direction and image sharpness in a sub-scanning direction, which problems may occur when the problems with regard to deterioration of image sharpness are reduced, are capable of being reduced.
The specific object of the present invention is to provide an apparatus for carrying out the image recording and read-out method.
The present invention provides a first image recording and read-out method, comprising the steps of:
i) locating an electromagnetic wave source, which produces a recording electromagnetic wave, on one side of an object,
ii) locating two-dimensional image read-out means on the other side of the object, the two-dimensional image read-out means comprising a charge accumulating section for accumulating latent image charges, which carry image information, and
iii) performing an operation for recording and reading out an image of the object,
wherein an anisotropic fluorescent material screen is located between the object and the two-dimensional image read-out means, and
the operation for recording and reading out the image of the object is performed in this state.
The anisotropic fluorescent material screen has a structure, in which an area filled with a fluorescent material is partitioned into a plurality of fine cells (fluorescent material-filled regions) by fluorescence reflecting partition wall members extending in the thickness direction of the screen. Specifically, the anisotropic fluorescent material screen may have a structure, in which the partition wall members and the fluorescent material-filled regions are arrayed alternately in a stripe-like form, and the fluorescent material-filled regions are thus arrayed to stand side by side in a one-dimensional direction. Alternatively, the anisotropic fluorescent material screen may have a structure, in which the fluorescent material-filled regions, i.e. the fine cells, partitioned from one another are distributed in two-dimensional directions. For example, the partition wall members may be arrayed in a checkered pattern.
In the latter case, plan shapes of the fluorescent material-filled regions, i.e., the cell shapes, as viewed from above the upper surface of the anisotropic fluorescent material screen, may be one of various shapes, such as square shapes and circular shapes.
By way of example, as the anisotropic fluorescent material screen, in which the fine cells are distributed in two-dimensional directions, one of the anisotropic fluorescent material screens described below may be employed.
Specifically, a first example is an anisotropic fluorescent material screen proposed by the applicant in Japanese Patent Application No. 2000-132356. The anisotropic fluorescent material screen comprises at least two striped fluorescent material layers, each of which is constituted of stripe-like partition walls for partitioning the anisotropic fluorescent material screen in a one-dimensional direction along a plane direction, and fluorescent material-filled regions partitioned by the stripe-like partition walls, the at least two striped fluorescent material layers being overlaid one upon the other such that the stripe-like partition walls of each of the striped fluorescent material layers intersect at an angle of approximately 90xc2x0 (i.e., approximately perpendicularly) or approximately 60xc2x0 with the stripe-like partition walls of an adjacent striped fluorescent material layer.
A second example is an anisotropic fluorescent material screen produced by a production process proposed by the applicant in Japanese Patent Application No. 2000-132355. The anisotropic fluorescent material screen is produced by a production process comprising the steps of:
a) forming a fluorescent material film, which is substantially constituted of a fluorescent material,
b) forming a plurality of grooves, each of which has a predetermined width, at predetermined intervals in the fluorescent material film,
c) filling each of the grooves with a composition, which contains a partition wall material dispersed therein,
d) solidifying the composition to obtain a striped fluorescent material film, which has partition walls arrayed so as to stand side by side in a one-dimensional direction, and
e) overlaying a plurality of striped fluorescent material films, which have thus been obtained, such that the stripes of each of the striped fluorescent material films intersect with the stripes of an adjacent striped fluorescent material film (and preferably thereafter applying heat and a pressure to the striped fluorescent material films, which have thus been overlaid one upon another).
A third example is an anisotropic fluorescent material screen produced by a production process proposed by the applicant in Japanese Patent Application No. 2000-132355. The anisotropic fluorescent material screen is produced by a production process comprising the steps of:
a) forming a fluorescent material film, which is substantially constituted of a fluorescent material,
b) forming a plurality of grooves, each of which has a predetermined width, at predetermined intervals in the fluorescent material film,
c) filling each of the grooves with a composition, which contains a partition wall material dispersed therein,
d) applying the composition, which contains the a partition wall material dispersed therein, onto a surface of the fluorescent material film,
e) solidifying the composition to obtain a striped fluorescent material film, which has partition walls arrayed so as to stand side by side in a one-dimensional direction and has a partition wall layer formed on one surface,
f) overlaying a plurality of striped fluorescent material films, which have thus been obtained, such that the stripes of each of the striped fluorescent material films are parallel with the stripes of an adjacent striped fluorescent material film, (and preferably thereafter applying heat and a pressure to the striped fluorescent material films, which have thus been overlaid one upon another,) to obtain a laminate block, and
g) slicing the laminate block along a lamination plane, in which the stripes appear.
The present invention also provides a second image recording and read-out method aiming at reducing a moire phenomenon occurring due to the provision of the anisotropic fluorescent material screen wherein, in cases where two-dimensional image read-out means, which is constituted of a plurality of linear electrodes arrayed in a stripe-like form, and an anisotropic fluorescent material screen, in which a direction of anisotropy is a one-dimensional direction alone, are utilized, the anisotropic fluorescent material screen is located such that no moire may occur in an array direction of the linear electrodes, along which the linear electrodes stand side by side. Specifically, the present invention also provides a second image recording and read-out method, comprising the steps of:
i) locating an electromagnetic wave source, which produces a recording electromagnetic wave, on one side of an object,
ii) locating two-dimensional image read-out means on the other side of the object, the two-dimensional image read-out means comprising a charge accumulating section for accumulating latent image charges, which carry image information,
iii) locating an anisotropic fluorescent material screen between the object and the two-dimensional image read-out means, and
iv) performing an operation for recording and reading out an image of the object,
wherein the two-dimensional image read-out means comprises a plurality of linear electrodes for acquiring an electric signal proportional to an amount of the latent image charges, the linear electrodes being arrayed so as to stand side by side in a stripe-like form,
the anisotropic fluorescent material screen is a fluorescent material screen, in which a direction of anisotropy is a one-dimensional direction alone, and
the anisotropic fluorescent material screen is located such that the direction of anisotropy is approximately normal to an array direction of the linear electrodes, along which the linear electrodes stand side by side.
The term xe2x80x9cdirection of anisotropyxe2x80x9d as used herein means the array direction of the fluorescence reflecting partition wall members, along which the partition wall members stand side by side, in the anisotropic fluorescent material screen.
The present invention further provides a third image recording and read-out method aiming at reducing the moire phenomenon occurring due to the provision of the anisotropic fluorescent material screen, wherein moire components, which may be contained in an image signal detected with the two-dimensional image read-out means, are reduced or eliminated. Specifically, the present invention further provides a third image recording and read-out method, comprising the steps of:
i) locating an electromagnetic wave source, which produces a recording electromagnetic wave, on one side of an object,
ii) locating two-dimensional image read-out means on the other side of the object, the two-dimensional image read-out means comprising a charge accumulating section for accumulating latent image charges, which carry image information,
iii) locating an anisotropic fluorescent material screen between the object and the two-dimensional image read-out means, and
iv) performing an operation for recording and reading out an image of the object,
wherein a difference between a spatial frequency of a read-out pitch (a sensor pitch) of an image signal detected with the two-dimensional image read-out means and a spatial frequency of an anisotropy pitch of the anisotropic fluorescent material screen is set at a value of at least 1 cycle/mm.
In the third image recording and read-out method in accordance with the present invention, signal components, which are contained in the image signal having been detected with the two-dimensional image read-out means and which carry a moire frequency occurring due to the anisotropic fluorescent material screen, should preferably be suppressed.
The term xe2x80x9cread-out pitch of an image signalxe2x80x9d as used herein means the read-out pitch PO, at which the image signal proportional to the amount of the latent image charges accumulated at the charge accumulating section is acquired. How the read-out pitch PO is defined varies for different constitutions of the two-dimensional image read-out means. For example, in cases where the improved direct conversion type of solid-state radiation detector is employed as the two-dimensional image read-out means, an array pitch PC of the linear electrodes of the solid-state radiation detector or a scanning pitch (sampling pitch) PS of the reading light is defined as the read-out pitch PO. In cases where the direct conversion type of solid-state radiation detector is employed as the two-dimensional image read-out means, an array pitch PD of the charge collecting electrodes of the solid-state radiation detector is defined as the read-out pitch PO. In cases where the photo conversion type of solid-state radiation detector is employed as the two-dimensional image read-out means, an array pitch PP of the photoelectric conversion devices of the solid-state radiation detector is defined as the read-out pitch PO.
The term xe2x80x9cspatial frequency of a read-out pitch of an image signalxe2x80x9d as used herein means the frequency represented by the formula of fO=1/PO, in which PO represents the read-out pitch. Also, the term xe2x80x9cspatial frequency of an anisotropy pitchxe2x80x9d as used herein means the frequency represented by the formula of fG=1/PG, in which PG represents the anisotropy pitch of the anisotropic fluorescent material screen, i.e. the array pitch of the partition wall members of the anisotropic fluorescent material screen. As described above, the read-out pitch PO varies for different constitutions of the two-dimensional image read-out means.
In cases where the anisotropy pitch PG and the read-out pitch PO are different from each other, even if uniform recording electromagnetic wave is irradiated to the two-dimensional image read-out means, a periodical streak-like pattern, i.e. a moire, occurs in the image due to a spatial phase difference. The term xe2x80x9cmoire frequency occurring due to an anisotropic fluorescent material screenxe2x80x9d as used herein means the repetition frequency of the streak-like pattern in the moire phenomenon. Specifically, in cases where the improved direct conversion type of solid-state radiation detector is employed as the two-dimensional image read-out means, the term xe2x80x9cmoire frequency occurring due to an anisotropic fluorescent material screenxe2x80x9d as used herein means the difference between a spatial frequency fC of the pitch of the linear electrodes of the solid-state radiation detector and the spatial frequency fG of the anisotropy pitch of the anisotropic fluorescent material screen, or the difference between a spatial frequency fS of the sampling pitch, at which the latent image charges are read with scanning in the longitudinal direction of each linear electrode, and the spatial frequency fG of the anisotropy pitch. In cases where the direct conversion type of solid-state radiation detector is employed as the two-dimensional image read-out means, the term xe2x80x9cmoire frequency occurring due to an anisotropic fluorescent material screenxe2x80x9d as used herein means the difference between a spatial frequency fD of the charge collecting electrodes of the solid-state radiation detector, which spatial frequency is taken in the array direction of the partition wall members of the anisotropic fluorescent material screen, and the spatial frequency fG of the anisotropy pitch of the anisotropic fluorescent material screen. In cases where the photo conversion type of solid-state radiation detector is employed as the two-dimensional image read-out means, the term xe2x80x9cmoire frequency occurring due to an anisotropic fluorescent material screenxe2x80x9d as used herein means the difference between a spatial frequency fP of the photoelectric conversion devices of the solid-state radiation detector, which spatial frequency is taken in the array direction of the partition wall members of the anisotropic fluorescent material screen, and the spatial frequency fG of the anisotropy pitch of the anisotropic fluorescent material screen. As described above, the read-out pitch PO varies for different constitutions of the two-dimensional image read-out means.
The present invention still further provides a fourth image recording and read-out method aiming at reducing the moire phenomenon occurring due to the provision of the anisotropic fluorescent material screen, wherein the read-out pitch of the two-dimensional image read-out means is set such that no moire component may occur. Specifically, the present invention still further provides a fourth image recording and read-out method, comprising the steps of:
i) locating an electromagnetic wave source, which produces a recording electromagnetic wave, on one side of an object,
ii) locating two-dimensional image read-out means on the other side of the object, the two-dimensional image read-out means comprising a charge accumulating section for accumulating latent image charges, which carry image information,
iii) locating an anisotropic fluorescent material screen between the object and the two-dimensional image read-out means, and
iv) performing an operation for recording and reading out an image of the object,
wherein a spatial frequency of a read-out pitch of an image signal detected with the two-dimensional image read-out means is set at a value at least two times as high as a spatial frequency of an anisotropy pitch of the anisotropic fluorescent material screen.
In the fourth image recording and read-out method in accordance with the present invention, signal components, which are contained in the image signal having been detected with the two-dimensional image read-out means and which carry the spatial frequency of the anisotropy pitch of the anisotropic fluorescent material screen, should preferably be suppressed.
The present invention also provides a fifth image recording and read-out method aiming at reducing the problems occurring in that image sharpness in a main scanning direction and image sharpness in a sub-scanning direction become unbalanced due to the provision of the anisotropic fluorescent material screen. Specifically, the present invention also provides a fifth image recording and read-out method, comprising the steps of:
i) locating an electromagnetic wave source, which produces a recording electromagnetic wave, on one side of an object,
ii) locating two-dimensional image read-out means on the other side of the object, the two-dimensional image read-out means comprising a charge accumulating section for accumulating latent image charges, which carry image information,
iii) locating an anisotropic fluorescent material screen, in which a direction of anisotropy is a one-dimensional direction alone, between the object and the two-dimensional image read-out means, such that the direction of anisotropy in the anisotropic fluorescent material screen coincides with a main scanning direction or a sub-scanning direction in the two-dimensional image read-out means, and
iv) performing an operation for recording and reading out an image of the object,
wherein sharpness of an image signal, which has been detected with the two-dimensional image read-out means, with respect to the main scanning direction and sharpness of the image signal with respect to the sub-scanning direction are set to be approximately identical with each other.
The present invention further provides an apparatus for carrying out the first image recording and read-out method in accordance with the present invention. Specifically, the present invention further provides a first image recording and read-out apparatus, comprising two-dimensional image read-out means for receiving an incident recording electromagnetic wave and accumulating latent image charges, which carry image information, at a charge accumulating section,
wherein the improvement comprises the provision of an anisotropic fluorescent material screen, which is located between an object and the two-dimensional image read-out means.
The two-dimensional image read-out means should preferably be a photo reading type of two-dimensional image read-out means operating such that, when the photo reading type of two-dimensional image read-out means is exposed to a reading electromagnetic wave, the photo reading type of two-dimensional image read-out means outputs an image signal of a level proportional to the amount of the latent image charges accumulated at the charge accumulating section. Particularly, in cases where the solid-state radiation detectors proposed by the applicant in, for example, Japanese Patent Application Nos. 10(1998)-232824, 10(1998)-271374, 11(1999)-87922, and 11(1999)-89553 are employed as the two-dimensional image read-out means, a high efficiency and a high resolution can be obtained.
The present invention still further provides an apparatus for carrying out the second image recording and read-out method in accordance with the present invention. Specifically, the present invention still further provides a second image recording and read-out apparatus, comprising:
i) an anisotropic fluorescent material screen, and
ii) two-dimensional image read-out means for receiving a recording electromagnetic wave incident via the anisotropic fluorescent material screen and accumulating latent image charges, which carry image information, at a charge accumulating section,
wherein the two-dimensional image read-out means comprises a plurality of linear electrodes for acquiring an electric signal proportional to an amount of the latent image charges, the linear electrodes being arrayed so as to stand side by side in a stripe-like form,
the anisotropic fluorescent material screen is a fluorescent material screen, in which a direction of anisotropy is a one-dimensional direction alone, and
the anisotropic fluorescent material screen is located such that the direction of anisotropy is approximately normal to an array direction of the linear electrodes, along which the linear electrodes stand side by side.
The present invention also provides an image recording and read-out apparatus, comprising:
i) an anisotropic fluorescent material screen, and
ii) two-dimensional image read-out means for receiving a recording electromagnetic wave incident via the anisotropic fluorescent material screen and accumulating latent image charges, which carry image information, at a charge accumulating section,
wherein the apparatus further comprises moire component reducing means for reducing moire components, which may be contained in an image signal detected with the two-dimensional image read-out means and which occur due to the anisotropic fluorescent material screen.
The term xe2x80x9creducing moire componentsxe2x80x9d as used herein means that the moire components contained in the image signal having been detected with the two-dimensional image read-out means are reduced or eliminated, and that the image signal is acquired such that no moire component may occur.
Specifically, the present invention further provides a third image recording and read-out apparatus for carrying out the third image recording and read-out method in accordance with the present invention, wherein the moire component reducing means is means for operating such that a difference between a spatial frequency of a read-out pitch of the image signal detected with the two-dimensional image read-out means and a spatial frequency of an anisotropy pitch of the anisotropic fluorescent material screen is set at a value of at least 1 cycle/mm.
In the third image recording and read-out apparatus in accordance with the present invention, the moire component reducing means should preferably be provided with first image processing means for suppressing signal components, which are contained in the image signal having been detected with the two-dimensional image read-out means and which carry a moire frequency occurring due to the anisotropic fluorescent material screen.
The present invention still further provides a fourth image recording and read-out apparatus for carrying out the fourth image recording and read-out method in accordance with the present invention, wherein the moire component reducing means is means for operating such that a spatial frequency of a read-out pitch of the image signal detected with the two-dimensional image read-out means is set at a value at least two times as high as a spatial frequency of an anisotropy pitch of the anisotropic fluorescent material screen.
In the fourth image recording and read-out apparatus in accordance with the present invention, the moire component reducing means should preferably be provided with second image processing means for suppressing signal components, which are contained in the image signal having been detected with the two-dimensional image read-out means and which carry the spatial frequency of the anisotropy pitch of the anisotropic fluorescent material screen.
The present invention also provides an apparatus for carrying out the fifth image recording and read-out method in accordance with the present invention. Specifically, the present invention also further provides a fifth image recording and read-out apparatus, comprising:
i) an anisotropic fluorescent material screen, in which a direction of anisotropy is a one-dimensional direction alone, and
ii) two-dimensional image read-out means for receiving a recording electromagnetic wave incident via the anisotropic fluorescent material screen and accumulating latent image charges, which carry image information, at a charge accumulating section,
the anisotropic fluorescent material screen being located such that the direction of anisotropy in the anisotropic fluorescent material screen coincides with a main scanning direction or a sub-scanning direction in the two-dimensional image read-out means,
wherein the apparatus further comprises sharpness balancing means for operating such that sharpness of an image signal, which has been detected with the two-dimensional image read-out means, with respect to the main scanning direction and sharpness of the image signal with respect to the sub-scanning direction are set to be approximately identical with each other.
In the fifth image recording and read-out method and the fifth image recording and read-out apparatus in accordance with the present invention, the sharpness of the image signal with respect to the main scanning direction and the sharpness of the image signal with respect to the sub-scanning direction are set to be approximately identical with each other. For such purposes, the sharpness with respect to a scanning direction, which is associated with a low sharpness, may be enhanced so as to become approximately identical with a high sharpness with respect to the other scanning direction, and the sharpness with respect to the two scanning directions may thereby be set to be approximately identical with each other. Alternatively, the sharpness with respect to a scanning direction, which is associated with a high sharpness, may be suppressed so as to become approximately identical with a low sharpness with respect to the other scanning direction, and the sharpness with respect to the two scanning directions may thereby be set to be approximately identical with each other.
With the first image recording and read-out method and the first image recording and read-out apparatus in accordance with the present invention, the anisotropic fluorescent material screen is located between the object and the two-dimensional image read-out means, which should preferably be of the photo reading type, and the operation for recording and reading out the image of the object is performed in this state. The fluorescence produced within the anisotropic fluorescent material screen diffuses in the fluorescent material-filled regions and becomes blurred. However, the fluorescence is reflected by the fluorescence reflecting partition wall members of the anisotropic fluorescent material screen. Therefore, with respect to the array direction of the fluorescence reflecting partition wall members, along which the partition wall members stand side by side, the fluorescence does not spread beyond the array pitch of the partition wall members. Accordingly, deterioration in sharpness with respect to the array direction of the fluorescence reflecting partition wall members, along which the partition wall members stand side by side, can be reduced.
With the second image recording and read-out method and the second image recording and read-out apparatus in accordance with the present invention, the anisotropic fluorescent material screen, in which the direction of anisotropy is the one-dimensional direction alone, is located such that the direction of anisotropy is approximately normal to the array direction of the linear electrodes, along which the linear electrodes stand side by side. Therefore, with respect to the array direction of the linear electrodes, along which the linear electrodes stand side by side, no moire occurs.
With the third image recording and read-out method and the third image recording and read-out apparatus in accordance with the present invention, the difference between the spatial frequency of the read-out pitch of the image signal detected with the two-dimensional image read-out means and the spatial frequency of the anisotropy pitch of the anisotropic fluorescent material screen is set at a value of at least 1 cycle/mm. Therefore, as will be described later, in cases where the spatial frequency fO of the read-out pitch cannot be set to be at least two times as high as the spatial frequency fG of the anisotropy pitch, the number of perceptible streaks periodically occurring in the obtained image can be decreased. In this manner, the moire occurring in the image can be rendered visually imperceptible.
In such cases, the signal components, which are contained in the image signal having been detected with the two-dimensional image read-out means and which carry the moire frequency occurring due to the anisotropic fluorescent material screen, should preferably be suppressed. In this manner, the moire occurring in the image can be rendered visually imperceptible. Also, in such cases, there is no risk that the important components of at most 1 cycle/mm, which are contained in the image information, will be lost.
With the fourth image recording and read-out method and the fourth image recording and read-out apparatus in accordance with the present invention, such that no moire component may occur, the spatial frequency of the readout pitch of the image signal detected with the two-dimensional image read-out means is set at a value at least two times as high as the spatial frequency of the anisotropy pitch of the anisotropic fluorescent material screen. Therefore, in accordance with the so-called xe2x80x9csampling theorem,xe2x80x9d theoretically, the streak-like pattern in the image due to the moire phenomenon do not occur.
In such cases, the streak-like pattern representing the partition wall members of the anisotropic fluorescent material screen appears in the obtained image. However, with the fourth image recording and read-out method and the fourth image recording and read-out apparatus in accordance with the present invention, wherein the signal components, which are contained in the image signal having been detected with the two-dimensional image read-out means and which carry the spatial frequency of the anisotropy pitch of the anisotropic fluorescent material screen, are suppressed, the streak-like pattern representing the partition wall members of the anisotropic fluorescent material screen can be rendered visually imperceptible.
With the fifth image recording and read-out method and the fifth image recording and read-out apparatus in accordance with the present invention, in cases where the anisotropic fluorescent material screen, in which the direction of anisotropy is the one-dimensional direction alone, is employed, the sharpness of the image signal, which has been detected with the two-dimensional image read-out means, with respect to the main scanning direction and the sharpness of the image signal with respect to the sub-scanning direction are set to be approximately identical with each other. Therefore, the problems can be prevented from occurring in that the sharpness with respect to the main scanning direction and the sharpness with respect to the sub-scanning direction become different from each other and thus become unbalanced.
With the image recording and read-out method and apparatus in accordance with the present invention, wherein the first example of the anisotropic fluorescent material screen having the structure, in which the stripe-like partition walls of each of the striped fluorescent material layers intersect at an angle of approximately 90xc2x0 with the stripe-like partition walls of an adjacent striped fluorescent material layer, is employed, the fluorescence produced in the top striped fluorescent material layer due to exposure to the radiation diffuses slightly in the direction parallel to the stripes and is prevented by the partition walls from diffusing in the direction normal to the stripes. In the next striped fluorescent material layer, the direction of restriction of the diffusion is reversed. As a result, as with a two-dimensional cell structure, a radiation image, in which the image quality with respect to the direction (the main scanning direction) normal to the stripes in the top striped fluorescent material layer and the image quality with respect to the direction (the sub-scanning direction) parallel to the stripes in the top striped fluorescent material layer are well-balanced, can be obtained. Therefore, the image recording and read-out method and apparatus in accordance with the present invention, wherein the first example of the anisotropic fluorescent material screen is employed, is advantageous particularly for use in a technique for forming a radiation image for medical diagnosis.
With the image recording and read-out method and apparatus in accordance with the present invention, wherein the first example of the anisotropic fluorescent material screen having the structure, in which the stripe-like partition walls of each of the striped fluorescent material layers intersect at an angle of approximately 60xc2x0 with the stripe-like partition walls of an adjacent striped fluorescent material layer, is employed, the aperture ratio is not reduced markedly, and a radiation image, in which the image quality with respect to the main scanning direction and the image quality with respect to the sub-scanning direction are well-balanced, can be obtained.
Also, in cases where the first example of the anisotropic fluorescent material screen is composed of two to ten striped fluorescent material layers overlaid one upon another, a radiation image, in which the image quality with respect to the main scanning direction and the image quality with respect to the sub-scanning direction are well-balanced, can be obtained, and the anisotropic fluorescent material screen can be produced reliably with a comparatively simple production process.
In cases where the second example of the anisotropic fluorescent material screen is employed, the formation of the fluorescent material film, the grooving, and the filling of the grooves with the composition containing the partition wall material can be performed continuously. Also, the anisotropic fluorescent material screen can be produced with three or four steps, i.e. the step of forming the fluorescent material film, the step of grooving, the step of filling the grooves with the composition containing the partition wall material (which step maybe performed simultaneously with the grooving step), and the step of overlaying the striped fluorescent material films one upon another. Therefore, the anisotropic fluorescent material screen can be produced with the process, which is simpler than conventional techniques and is composed of smaller number of steps than with the conventional techniques.
In cases where the third example of the anisotropic fluorescent material screen is employed, the formation of the fluorescent material film, the grooving, the filling of the grooves with the composition containing the partition wall material, and the formation of the partition wall layer can be performed continuously. Also, the anisotropic fluorescent material screen can be produced with four or five steps, i.e. the step of forming the fluorescent material film, the step of grooving, the step of filling the grooves with the composition containing the partition wall material (which step may be performed simultaneously with the grooving step), the step of overlaying the striped fluorescent material films one upon another, and the step of slicing. Therefore, the anisotropic fluorescent material screen can be produced with the process, which is simpler than the conventional techniques and is composed of smaller number of steps than with the conventional techniques.